...because after clarifying that their 9/22 order was only a temporary stay pending a review, the full 8th Circuit DENIED Missouri's request to freeze the District Court's ruling that the law was unconstitutional, pending the state's appeal of that decision:
Planned Parenthood withdraws application in Missouri case
A challenge to two Missouri abortion requirements has ended its trip to the Supreme Court at least for now. Attorneys for Planned Parenthood notified the Supreme Court tonight that they were withdrawing their request to block a ruling by the U.S. Court of Appeals for the 8th Circuit after that court ruled in the groups favor. Todays order means that a decision by a federal district judge that blocked the state from enforcing two of its abortion requirements can go into effect while the state appeals the district courts ruling.
http://www.scotusblog.com/2017/10/planned-parenthood-withdraws-application-missouri-case/
This was never going to be up to Gorsuch alone. If he denied their request, PP would have requested that another justice take a look at it. On the most contentious topics (i.e. abortion, death penalty stays, gay rights), the justice for the district that gets the initial request usually refers it promptly to the full court to stay everyone's time. (At most, they might ask for the other party to respond to the issue, since that's generally needed.) I don't know if he would have done that as it's convention not an actual 'rule', but the next judge would have.